The present invention relates to agricultural balers, and, more particularly, to an agricultural baler with retractable friction blocks in the ceiling and walls of the bale chamber.
Agricultural balers are used to consolidate and package crop material so as to facilitate the storage and handling of the crop material for later use. In the case of hay, a mower-conditioner is typically used to cut and condition the crop material for windrow drying in the sun. In the case of straw, an agricultural combine discharges non-grain crop material from the rear of the combine defining the straw (such as wheat or oat straw) which is to be picked up by the baler. The cut crop material is typically raked and dried, and a baler, such as a large square baler or round baler, straddles the windrows and travels along the windrows to pick up the crop material and form it into bales.
On a large square baler, a pickup unit at the front of the baler gathers the cut and windrowed crop material from the ground. The pickup unit includes a pickup roll, and optionally may include other components such as side shields, stub augers, wind guard, etc. A packer unit is used to move the crop material from the pickup unit to a duct or pre-compression chamber. The packer unit forms a wad of crop within the pre-compression chamber which is then transferred to a main bale chamber. For purposes of discussion, the charge of crop material within the pre-compression chamber will be termed a “wad”, and the charge of crop material after being compressed within the main bale chamber will be termed a “flake”. Typically such a packer unit includes packer tines or forks to move the crop material from the pickup unit into the pre-compression chamber. Instead of a packer unit it is also known to use a rotor cutter unit which may chop the crop material into smaller pieces.
A stuffer unit transfers the wad of crop material in charges from the pre-compression chamber to the main bale chamber. Typically such a stuffer unit includes stuffer forks which are used to move the wad of crop material from the pre-compression chamber to the main bale chamber, in sequence with the reciprocating action of a plunger within the main bale chamber. In the main bale chamber, after the wad is injected into the bale chamber, the plunger compresses the wad of crop material into a flake against previously formed flakes to form a bale and, at the same time, gradually advances the bale toward the outlet end of the bale chamber.
The bale chamber typically has three moving walls, being the top and two sides, which may be positioned by two hydraulically controlled actuators connected to a positioning mechanism. Pressure exerted by the walls of the bale chamber dictates the frictional force required to overcome static friction and shift the flakes in the chamber. An increased force to shift the flakes causes the plunger to compact the flakes tighter, to thereby produce a higher density bale.
When enough flakes have been added and the bale reaches a full or other predetermined size, a number of knotters are actuated which wrap and tie twine, cord or the like around the bale while it is still in the main bale chamber. The twine is cut and the formed baled is ejected out the back of the baler as a new bale is formed.
Under normal conditions, this arrangement works well, as the friction force of the ceiling and walls against the bale being compressed provides the back pressure necessary to achieve the desired density of crop material in the bale. However, under difficult baling conditions, insufficient back pressure may be present near the inlet end of the bale chamber nearest the plunger. As a result, the crop material may re-expand toward the plunger after the plunger has compressed it. Additionally, the ceiling may be pressed too low by the hydraulically controlled actuators, resulting in a poor bale shape, and binder twine snapping due to re-expansion of the crop material due to insufficient compression after the bale leaves the large square baler. Similarly, one or both of the walls may be pressed too far inward by the hydraulically controlled actuators, with similar results.
What is needed in the art is a way to increase the back pressure on the bale being formed and compressed near the inlet end of the bale chamber nearest the plunger, in order to cause the bale to fill the entire cross section of the bale chamber, and to achieve greater compression and higher density of the crop material.